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    #1

    Alternator Diodes Failed?

    I had my car's alternator tested at O'reilly a while ago. They told me that the diodes in the alt. were bad, and the whole thing would need to be replaced, and if not it would take out the voltage regulator. I have seen info online saying I can replace just the diodes, but I'm not sure. Any suggestions?

    I don't hear any whine in the radio, but things like the locks dim the lights. I have had the battery die on me if I leave the car off for a few weeks.
    MyTechtime
    1984 Lincoln Town Car
    Tags: None
    #2
    If it's drawing current on the charge cable when the car is off, there's at least 1 diode bad on the rectifier that's shorting to ground. You can replace just the diodes, buy unless you can test them individually after taking the alternator apart, you won't get anywhere. You can also replace the entire rectifier and rebuild the alternator yourself, but I'd rather just replace the alternator with one that has a lifetime warranty. If it's a 2g, upgrade to a 3g.

    Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
    rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

    Originally posted by gadget73
    ... and it should all work like magic and unicorns and stuff.

    Originally posted by dmccaig
    Overhead, some poor bastards are flying in airplanes.

    Comment

      #3
      You can do it, but its kind of difficult. They solder in there with a fairly fat iron, and as mentioned unless you know how to test them to figure which is bad you end up replacing all of them. There are 3 or 6, depending if they doubled them up for current capacity or not. I do not know whats in the 65 amp, but I'm pretty sure the 100 amp at least has dual rectifiers per phase. I've rebuilt alternators myself before but rebuilding the rectifier stack is more bother than I'm interested in. Bearings and brushes are about my limit of interest. A junkyard 3G would be my go-to before the rectifier stack.


      An 84 should be a 50 amp alternator, which is quite frankly just pathetic. They have lousy output when working 100%, and it gets considerably worse when a rectifier fails. Figure you've lost about 1/3 of your charge capacity, so it ends up being a 35 amp.
      86 Lincoln Town Car (Galactica).
      5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

      91 Lincoln Mark VII LSC grandpa spec white and cranberry

      1984 Lincoln Continental TurboDiesel - rolls coal

      Originally posted by phayzer5
      I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

      Comment

        #4
        I have A/C, so mine is a 60 amp. A new alternator is about $130, while a diode kit is about $50.
        MyTechtime
        1984 Lincoln Town Car

        Comment

          #5
          +1 on the 3G upgrade. It's not hard to do, and it's a worthwhile mod. The lights don't dim all the time, the rear defroster works better, etc.
          1990 MGM: $50 E7 heads, HO cam, Holley SysteMAX lower intake, HO upper intake with an Explorer TB. LSC ECM. Lincoln logs into stock dual exhaust. K&N drop in air filter. Wide ratio AOD, 2400 converter with a 3.08 one tire fire out back. Car is less slow now. Then there's the '92 Beater. Dual 2.25" exhaust with shiny tips. Rumbles nice. Super slow. Burns oil too.

          Comment

            #6
            Junkyard 3G, the cable and the fuse is probably no more than $50, and you get an alternator that has idle speed output.

            If you're in there doing diodes, replace the brushes and the bearings.
            86 Lincoln Town Car (Galactica).
            5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

            91 Lincoln Mark VII LSC grandpa spec white and cranberry

            1984 Lincoln Continental TurboDiesel - rolls coal

            Originally posted by phayzer5
            I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

            Comment

              #7
              Jy 3g around here is about $50 alone... but still much more reliable than a 2g and more power.

              Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
              rides: 93 Crown Vic LX (The Red Velvet Cake), 2000 Crown Vic base model (Sandy), 2003 Expedition (the vacation beast)

              Originally posted by gadget73
              ... and it should all work like magic and unicorns and stuff.

              Originally posted by dmccaig
              Overhead, some poor bastards are flying in airplanes.

              Comment

                #8
                Yep, 3g it and call it good.
                2020 F250 - 7.3 4x4 CCSB STX 3.55's - BAKFlip MX4
                2005 Grand Marquis GS - Marauder sway bars, Marauder exhaust, KYB's
                2003 Marauder - Trilogy # 8, JLT, kooks, 2.5" exhaust, 4.10's/31 spline, widened rear's, metco's, addco's, ridetech's 415hp/381tq
                1987 Colony Park - 03+ frame swap, blown Gen II Coyote, 6R80, ridetechs, stainless works, absolute money pit. WIP

                Comment

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